Silicone rubber composition for treatment of fiber structures

ABSTRACT

The silicone rubber compositions of the present invention for treatment of fiber structures are cured by a condensation reaction and are thus free from drawbacks of addition reaction curing type. The compositions contain mercaptoalkyl group-containing di- or trialkoxysilanes and aliphatic monohydroxy alcohols. As a result, even when inorganic filler content is increased in dispersion, viscosity stability was excellent, and high-strength films are readily obtained. Condensation reaction-curable silicone rubbers for treatment of fiber structure are provided which have excellent abrasion resistance and a pot life above 8 hours.

BACKGROUND OF THE INVENTION

The present invention concerns silicone rubber compositions fortreatment of fiber structures, such as woven fabric, knit fabric,nonwoven fabric, etc. More specifically, the present invention relatesto silicone rubber compositions for treatment of fiber structures,having long pot life and imparting films of excellent tensile strength,tear strength, and abrasion resistance.

Fiber structures, such as woven fabrics, knit fabrics and nonwovenfabrics, treated (especially coated) with conventional silicone rubbersare soft with excellent water-repellency, water-pressure resistance andalso high moisture permeability. Thus they have been widely used indiaper covers, snow wear, mountain wear, sports wear, raincoats, tents,etc.

The silicone rubbers used for coating fiber structures are, e.g.,addition reaction-curable silicone rubbers (Japanese Kokai Patents Nos.Sho 58(1983)-171937, Sho 60(1985)-51754 and Sho 57(1982)-165069) andcondensation reaction-curable silicone rubber (Japanese Kokai Patent No.Sho 53(1978)-94693).

However, the silicone rubbers have some strong points and also some weakpoints, and both long pot life and desirable physical properties cannotbe obtained at the same time.

For example, addition reaction-curable silicone rubbers form films withgood tensile strength, tear strength, abrasion resistance, etc., whiletheir adhesion to fiber structure is weak, and curing may be adverselyaffected by small amounts of surfactants and other impurities ofphosphorus, nitrogen, sulfur compounds adhered to the fiber duringprocessing of fibers or fabrics.

On the other hand, the condensation reaction-curable silicone rubbersshow good adhesion to the fiber structure, while tensile strength, tearstrength and abrasion resistance are not sufficient.

In the case of condensation reaction-curable silicone rubbers based onhydroxy-terminated organopolysiloxanes and organohydrogenpolysiloxanes,such drawbacks may be overcome by compounding inorganic reinforcingfillers such as finely powdered silica; while with increasing silicacontent, pot life decreases, and gelation occurs within 30 minutes, thuscoating workability is poor.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to overcome the above-notedproblems and provide condensation reaction-curable silicone rubbers fortreatment of fiber structure, having excellent abrasion resistance and apot life above 8 hours.

Such objectives can be attained by a silicone rubber composition fortreatment of fiber structures comprising:

(A) 100 parts by weight of an hydroxy group-terminatedorganopolysiloxane,

(B) 0-50 parts by weight of an alkenyl group-terminatedorganopolysiloxane,

(C) 3-100 parts by weight of an inorganic filler,

(D) 0.1-20 parts by weight of an organohydrogenpolysiloxane,

(E) 0.1-20 parts by weight of a di- or trialkoxysilane containing amercaptoalkyl group,

(F) 0.1-30 parts by weight of an aliphatic monohydroxy alcohol,

(G) 0.1-20 parts by weight of a curing catalyst, and

(H) an appropriate amount of solvent.

DETAILED DESCRIPTION OF THE INVENTION

The organopolysiloxane used for the component A is the main component ofthe coating materials of the present invention and is essentially alinear polysiloxane represented by the general formula HO(R₂ SiO)_(n) Hwherein R is a substituted or unsubstituted monovalent hydrocarbon groupand the subscript n is a number in the 50-10,000 range.

R represents an alkyl group such as methyl, ethyl, propyl, butyl, octyl,etc.; an alkenyl group such as vinyl, allyl, etc.; an aryl group such asphenyl, tolyl, etc.; a substituted alkyl group such as3,3,3-trifluoropropyl, 3-chloropropyl, etc.

While n is in the range of 50-10,000, those values of n above 1,000,known as organopolysiloxane rubbers, are preferred. Essentially linearmeans that unless there are some adverse effects, branched, cyclic andthree-dimensional structures may be present. All R groups may be thesame or different; however, it is preferred that a majority of the Rgroups be alkyl, most preferably methyl. Organopolysiloxane A may be ahomopolymer, a copolymer, or mixtures of two or more polymers.

The alkenyl group-terminated organopolysiloxane of component B is not anessential component; however, it enhances the elongation of the filmwhen cured together with the component A. A vinyl group is especiallypreferred for alkenyl group. Other organic groups include those givenfor R above. As with component A, the degree of polymerization ispreferably above 50, more preferably above 1,000, namely,organopolysiloxane rubber. Based on 100 parts by weight of component A,the amount of component B added is 0-50 parts by weight, preferably 5-30parts by weight.

The inorganic fillers used as component C are needed for enhancingtensile strength, tear strength and abrasion resistance of cured film.While fumed silica is preferred, dry-process silica, wet-process silica,finely powdered quartz, titanium dioxide, calcium carbonate, kieselguhr,carbon black, etc., can be also be used. They may be use as mixtures oftwo or more, and they may be surface-treated with silanes, silazanes,low-molecular-weight polysiloxanes, organic compounds, etc. Based on 100parts by weight of component A, the amount of component C added is 3-100parts by weight, preferably 5-50 parts by weight.

The organopolysiloxane used as component D in the present invention isthe crosslinking agent for component A and is linear, branched, orcyclic organohydrogenpolysiloxane of units of general formula R_(a)H_(b) SiO.sub.(4-a-b)/2 wherein R is substituted or unsubstitutedmonovalent hydrocarbon group as defined above; a is 1-3; b is 0.5-1,containing at least 3 hydrogen atoms bonded to different silicon atoms.Preferred are linear, branched and cyclic methylhydrogenpolysiloxanes,dimethyl-co-methylhydrogenpolysiloxanes, methylphenyl-co-methylhydrogenpolysiloxanes, etc., with a degree of polymerization 4-50. Based on 100parts by weight of component A, the amount of component D used is 0.1-20parts by weight, preferably 0.5-10 parts by weight.

The mercaptoalkyl group-containing di- or trialkoxysilane used ascomponent E in the present invention is needed for pot life extensionand can be represented by the general formula HS(CH₂)_(d) Si(R)_(e)(OR¹)_(3-e) wherein R is a substituted or unsubstituted monovalenthydrocarbon group as given above; R¹ is an alkyl group of 1-5 carbonatoms; d is 2-6; e is 0 or 1. Preferably, d is 3, and R or R¹ is analkyl group of 1-3 carbon atoms. Specific examples include HS(CH₂)₃Si(CH₃)(OCH₃)₂, HS(CH₂)₃ Si(CH₃)(OC₂ H₅)₂, HS(CH₂)₃ Si(CH₃)(OC₃ H₇)₂,HS(CH₂)₃ Si(OCH₃)₃, HS(CH₂)₃ Si(OC₂ H₅)₃, HS(CH₂)₃ Si(OC₃ H₇)₃, HS(CH₂)₅Si(OCH₃)₃, HS(CH₂)₃ Si(CH₃)(OC₄ H₉)₂, etc. Based on 100 parts by weightof component A, the amount of component E used is 0.1-20 parts byweight, preferably 0.5-10 parts by weight.

The aliphatic monohydroxy alcohol used as component F is also a potlife-extending component used with component E; aliphatic monohydroxyalcohols of 1-5 carbon atoms are preferred. Especially, for component F,monohydroxy alcohols of 1-3 carbon atoms are preferred because they arereadily evaporated upon heating without leaving any residues on fibersor any odor. Ethyl alcohol is most preferred. Based on 100 parts byweight of component A, the amount of component F used is 0.1-30 parts byweight, preferably 0.5-20 parts by weight.

The curing catalyst used for component G is a condensation reactioncatalyst and promotes reaction between component A (also component B ifpresent) and component D. The condensation reaction catalysts areorganometallic catalysts and amine catalysts. Organometallic catalystsare metal salts of organic acids, e.g., dibutyltin diacetate, dibutyltindilaurate, dioctyltin dilaurate, dibutyltin dioctoate, zinc naphthenate,tin octylate, cobalt octylate, diisooctyltin dioctylate, zirconiumnaphthenate, zirconium octylate, tetrabutyl orthotitanate, etc. Aminecatalysts are, e.g., di- and triethanolamine. Based on 100 parts byweight of component A, the amount of component F used is 0.2-20 parts byweight, preferably 0.5-10 parts by weight.

The solvents used as component H in the present invention are used inmaking the compositions of the present invention into dispersions foreasy application on fiber structure, e.g., aromatic hydrocarbon solventssuch as toluene, xylene, benzene, etc.; chlorine-containing solventssuch as carbon tetrachloride, trichloroethylene, 1,1,1-trichloroethane,tetrachloroethylene, etc.; aliphatic hydrocarbon solvents such ashexane, heptane, etc. Among them, aromatic solvents and chlorinesolvents are preferred. While the amount of component H used varies asneeded for ease of coating application, it is usually 50-2,000 parts byweight, preferably 100-1,000 parts by weight based on 100 parts byweight of component A.

In the present invention, beside components A-H, various additives maybe added, such as various silane couplers for enhanced adhesion,hydroxy-terminated low-molecular-weight organopolysiloxanes asplasticizers, triorganosilyl group-terminated silicone oils forimparting lubricity and softness to the film, pigments, dyes, antimildewagents, etc.

The fiber structures are woven, knit, nonwoven fabrics, etc., of naturalfibers such as cotton, jute, wool, silk, etc., regenerated fibers suchas rayon, semisynthetics such as acetate, etc., synthetic fibers such asnylons, polyesters, acrylics, vinyl chloride, polyethylene,polypropylene, Spandex, etc., and their blends.

The mode of application on fiber structures is not restricted in anyparticular way, while in a preferred process, films are formed bygravure or knife coating on the fiber structure and cured by heat. Ifdesired, a silicone rubber composition of the present invention iscoated on a Teflon sheet, etc., adhered to a fiber structure andheat-cured for adhesion of the silicone rubber to the fiber structure.Depending on the applications, immersion or spray method may be used.After solvents are evaporated, the treated fiber structures are heatedat 100°-200° C. for 1-5 min to form a silicone rubber film on the fiberstructure, with good toughness and moisture permeability.

The fiber structure treated with the silicone rubber compositions of thepresent invention have good toughness and moisture permeability, thusare useful for diaper covers, snow wear, mountain wear, sports wear,raincoat, tent, etc.

Next, the present invention is explained with examples. In the examples,parts and % are by weight.

APPLICATION EXAMPLES 1 AND 2

In a kneader mixer, 100 parts of hydroxy-terminated dimethylpolysiloxaneof molecular weight about 520,000, 9 parts of hydroxy-terminateddimethylpolysiloxane plasticizer with degree of polymerization 10, and30 parts of fumed silica (Aerosil 300, product of Nippon Aerosil Co.) ofspecific surface area 300 m² /g were kneaded sufficiently and heated at180° C. for 4 h to give a rubber base (I).

Using a stirrer 100 parts of this rubber base (I) were compounded with3.2 parts of trimethylsilyl-terminated methylhydrogenpolysiloxane withdegree of polymerization about 50 and 246.8 parts of toluene to givedispersion (I). This dispersion was rapidly stir-mixed with 1.0 part ofHS(CH₂)₃ Si(CH₃)(OCH₃)₂, 1.5 parts of methyl alcohol or 1.5 parts ofisopropyl alcohol, 1.0 part of dibutyltin di(2-ethylhexoate) catalyst,and 25 parts of toluene for viscosity control. Then changes in viscositywith elapse of time was measured using a single cylinder rotatingviscometer, Bisumetoron VG-A (product of Seiki Industrial Co., Ltd.).After 10 h, the dispersion was coated on a polytetrafluoroethylene(Teflon) film using a 100-μm applicator, and the ease of coatingapplication was examined. Next, most of toluene was removed by blowinghot air, and a nylon taffeta was spread on the coating. Then, thesilicone rubber was cured by heating in a hot-air circulation oven at150° C. for 5 min. The assembly was then cooled to room temperature, andthe Teflon film was peeled from the silicone rubber-coated nylontaffeta. The silicone coating film was examined.

For comparison, the experiment was repeated without methyl alcohol orHS(CH₂)₃ Si(CH₃)(OCH₃)₂ or both. In all cases, gelation occurredquickly, while the composition of the present invention, using bothmethyl alcohol and HS(CH₂)₃ Si(CH₃)(OCH₃)₂ showed stable viscosity evenafter 10 h with good coating workability, giving coated films free fromvoids. The results are given in Table I.

                  TABLE I                                                         ______________________________________                                                    Application                                                                             Comparative                                                         Example   Example                                                             1     2       1       2    3                                      ______________________________________                                        Composition, parts                                                            Dispersion     100     100     100   100  100                                 HS(CH.sub.2).sub.3 SiMe(OMe).sub.2                                                          1.0     1.0     --    --   1.0                                  Methanol      1.5     --      --    1.5  --                                   Isopropanol   --      1.5     --    --   --                                   Properties                                                                    Change of Viscosity                                                           (cP) with time                                                                 0 Hours      8200    8400    9200  8700 9050                                  0.5 Hours    8100    8200    gel   gel  8800                                  1 Hours      8100    8200    --    --   9000                                  2 Hours      8050    8200    --    --   15000                                 3 Hours      8350    8300    --    --   gel                                   5 Hours      8350    8350    --    --   --                                    8 Hours      8350    8300    --    --   --                                   10 Hours      8400    8350    --    --   --                                   State of Coating                                                                            good    good    poor  poor poor                                 after 10 hours                                                                Surface State good    good    --    --   --                                   of film                                                                       ______________________________________                                    

APPLICATION EXAMPLES 3-6

The dispersion (I) used in Application Example 1 was treated with 1.5parts of ethyl alcohol and various amounts of HS(CH₂)₃ Si(CH₃)(OCH₃)₂.Then changes in viscosity with time was measured as in ApplicationExample 1 with observation of states of coating and film. Forcomparison, the process was repeated using 1.5 parts of ethyl alcohol,but without HS(CH₂)₃ Si(CH₃)(OCH₃)₂. The results are given in Table II.The composition with only ethyl alcohol was found to be gelled after 30min, while the compositions treated with both ethyl alcohol and HS(CH₂)₃Si(CH₃)(OCH₃)₂ showed stable viscosity even after 10 hours with goodcoatability and state of film.

                  TABLE II                                                        ______________________________________                                                    Application   Comparative                                                     Example       Example                                                         3    4      5      6    4                                         ______________________________________                                        Composition, parts                                                            Dispersion     100    100    100  100  100                                    HS(CH.sub.2).sub.3 SiMe(OMe).sub.2                                                          .25    .50    1.0  2.0  --                                      Ethanol       1.5    1.5    1.5  1.5  1.5                                     Properties                                                                    Change of Viscosity                                                           (cP) with time                                                                 0 Hours      9200   9050   8400 7800 9250                                     0.5 Hours    9200   8750   8350 7800 gel                                      1 Hours      9350   8750   8350 7500 --                                       2 Hours      9400   8750   8500 7500 --                                       3 Hours      9500   8700   8400 7500 --                                       5 Hours      9500   8700   8350 7500 --                                       8 Hours      9450   8650   8350 7700 --                                      10 Hours      9550   8750   8500 7600 --                                      State of Coating                                                                            good   good   good good poor                                    after 10 hours                                                                Surface State good   good   good good --                                      of film                                                                       ______________________________________                                    

APPLICATION EXAMPLES 7-10

Rubber base (II) was prepared under the conditions of ApplicationExample 1, except that 90 parts of the hydroxy-terminateddimethylpolysiloxane with molecular weight 520,000 used in ApplicationExample 1 and 10 parts of vinyl group-terminated dimethylpolysiloxane ofmolecular weight 55000 were used.

Dispersion (II) was prepared under the same conditions of ApplicationExample 1 from 100 parts of the rubber base (II).

Then, 100 parts of dispersion (II) was treated with 1 part of dibutyltindiacetate catalyst and 25 parts of toluene as viscosity control agent.As shown in Table III, the mixture was stirred with 2 parts of HS(CH₂)₃Si(CH₃)(OCH₃)₂, 0.5, 2.5, or 5.0 parts of ethyl alcohol. Similar toApplication Example 1, the change in viscosity with time was measuredand coating films were prepared.

An experiment was also carried out using 2.0 parts of HS(CH₂)₃ Si(OCH₃)₃and 1.0 part of ethyl alcohol. A comparative example was made using 2.0parts of HS(CH₂)₃ Si(OCH₃)₃ without ethyl alcohol.

The results are given in Table III. Compared with the comparativeexample, the examples of the present invention showed stable viscosityeven after 24 h with good state of films.

                  TABLE III                                                       ______________________________________                                                    Application   Comparative                                                     Example       Example                                                         7    8      9      10   5                                         ______________________________________                                        Composition, parts                                                            Dispersion (II)                                                                              100    100    100  100  100                                    HS(CH.sub.2).sub.3 SiMe(OMe).sub.2                                                          2.0    2.0    2.0  --   --                                      HS(CH.sub.2).sub.3 Si(OMe).sub.3                                                            --     --     --   2.0  2.0                                     Ethanol       0.5    2.5    5.0  1.0  --                                      Properties                                                                    Change of Viscosity                                                           (cP) with time                                                                 0 Hours      8450   7400   6800 7880 8350                                     1 Hours      8450   7400   6800 7880 8660                                     2 Hours      8650   7300   6800 7750 12350                                    5 Hours      8350   7300   6950 7820 gel                                     10 Hours      8600   7650   6800 7950 --                                      24 Hours      8950   7850   7450 7980 --                                      State of Coating                                                                            good   good   good good poor                                    after 24 hours                                                                Surface State good   good   good good --                                      of film                                                                       ______________________________________                                    

APPLICATION EXAMPLES 11-14

Rubber bases (III), (IV), (V), and (VI) were prepared from 90 parts ofdimethyl polysiloxane having hydroxyl groups at the ends of molecularchains with molecular weight of about 520,000 used in ApplicationExample 3, 10 parts of dimethyl polysiloxane having vinyl groups at theends of molecular chains with molecular weight of about 55,000 used inApplication Example 3, as well as 5.25 parts (5% with respect to theweight of polysiloxane), 11.11 parts (10% with respect to the weight ofpolysiloxane), 17.64 parts (15% with respect to the weight ofpolysiloxane), and 25.0 parts (20% with respect to the weight ofpolysiloxane) of fumed silica and a specific surface area of 300 m² /g(Aerosil 300, Nippon Aerosil Co., Ltd), respectively. As a comparativeexample, rubber base (VVI) was prepared without adding the fumed silica.For each rubber base 100 parts were taken to prepare dispersions(III)-(VII) according to Application Example 1. In Application Example1, 25 parts of toluene were added to 100 parts of the dispersion. Inthis case, however, it was not added, while 1.0 part of dibutyltindi(2-ethylhexoate) as well as 2.0 part of HS(CH₂)₃ Si(CH₃)(OCH₃)₂ listedin Table IV and 3.0 parts of ethyl alcohol were added. For the obtainedsample, the variation in time of the viscosity was measured in the sameway as in Application Example 1.

The above dispersions containing HS(CH₂)₃ Si(CH₃)(OCH₃)₂ and ethylalcohol were cast into a Teflon mold of 11×15×0.5 cm and allowed tostand at room temperature for 2 days for evaporation of the solvent thenheated in a circulation hot-air oven at 150° C. for 5 min to obtainsilicone rubber sheets. These silicone rubber sheets were made into testspecimens using a dumbbell puncher. The specimens were tested fortensile strength using a tensile tester at a rate of 30 cm/min.

Usually, an increase in fumed silica content results in poor viscositystability of dispersions. However, as shown in Table IV, in the examplesof the present invention, even with increased fumed silica content, theinitial viscosity shows no changes even after 24 h. Since the filmtensile strength increases with increasing fumed silica content, thepresent invention provides both stable dispersion viscosity and siliconerubber films of high strength.

                  TABLE IV                                                        ______________________________________                                                    Application   Comparative                                                     Example       Example                                                         11   12     13     14   6                                         ______________________________________                                        Composition, parts                                                            Dispersion, 100                                                                             (III)  (IV)   (V)  (VI) (VII)                                   Fume Silica, % of                                                                             5     10      15   20   0                                     Polysiloxane                                                                  HS(CH.sub.2).sub.3 SiMe(OMe).sub.2                                                          2.0    2.0    2.0  2.0  2.0                                     Ethanol       3.0    3.0    3.0  3.0  3.0                                     Properties                                                                    Change of Viscosity                                                           (cP) with time                                                                 0 Hours      7400   9200   12250                                                                              17550                                                                              6300                                     1 Hours      7400   9200   12250                                                                              17550                                                                              6300                                     2 Hours      7300   9000   11150                                                                              16600                                                                              6100                                     5 Hours      7250   8600   12200                                                                              15500                                                                              6050                                    10 Hours      7950   8900   12250                                                                              17850                                                                              6350                                    24 Hours      7900   9300   11700                                                                              17200                                                                              6550                                    State of Coating                                                                            good   good   good good good                                    after 10 hours                                                                Surface State good   good   good good good                                    of film                                                                       Tensile Strength,                                                                           25.5   40.3   57.3 80.5 9.8                                     kg/cm.sup.2                                                                   Overall rating as                                                                           *      *      *    *    **                                      coating material                                                              ______________________________________                                         *Suitable                                                                     **Unsuitable                                                             

EFFECTS OF THE INVENTION

The condensation reaction-curing silicone rubber compositions of thepresent invention containing mercaptoalkyl group-containing di-ortrialkoxysilanes and aliphatic monohydroxy alcohols are free fromdrawbacks of addition reaction curing type and, even when inorganicfiller content is increased in dispersion, viscosity stability wasexcellent, and high-strength films are readily obtained.

That which is claimed is:
 1. A silicone rubber composition for treatmentof fiber structures consisting essentially of:(A) 100 parts by weight ofa hydroxy group-terminated organopolysiloxane, (B) 0-50 parts by weightof an alkenyl group-terminated organopolysiloxane, (C) 3-100 parts byweight of an inorganic filler, (D) 0.1-20 parts by weight of anorganohydrogenpolysiloxane, (E) 0.1-20 parts by weight of a di- ortrialkoxysilane containing a mercaptoalkyl group, (F) 0.1-30 parts byweight of an aliphatic monohydroxy alcohol, (G) 0.1-20 parts by weightof a curing catalyst, and (H) an appropriate amount of solvent.
 2. Asilicone rubber composition in accordance with claim 1 wherein component(A) is an organopolysiloxane rubber.
 3. A silicone rubber composition inaccordance with claim 1 wherein alkenyl group of the component (B) isvinyl group.
 4. A silicone rubber composition in accordance with claim 1wherein component (C) is finely divided silica.
 5. A silicone rubbercomposition in accordance with claim 1 wherein component (E) is analkylmercaptopropyldialkoxysilane or a mercaptopropyltrialkoxysilanewith alkyl and alkoxy groups of 1-3 carbon atoms.
 6. A silicone rubbercomposition in accordance with claim 1 wherein component (F) is analiphatic monohydroxy alcohol of 1-5 carbon atoms.
 7. A silicone rubbercomposition in accordance with claim 1 wherein component (A) is ahydroxy group-terminated polydimethylsiloxane, component (B) is analkenyl group-terminated polydimethylsiloxane and component (D) is amethylhydrogenpolysiloxane.
 8. A silicone rubber composition inaccordance with claim 1 wherein component (G) is a metal salt of anorganic acid.
 9. A silicone rubber composition in accordance with claim1 wherein the component (A) is a hydroxy group terminatedpolymethylsiloxane rubber, component (B) is an alkenyl group-terminatedpolydimethylsiloxane, component (C) is finely divided silica, component(D) is a polymethylhydrogensiloxane, component (E) ismethylmercaptopropyldimethoxysilane or mercaptopropyltrimethoxysilane,component (F) is an aliphatic monohydroxy alcohol of 1-3 carbon atomsand component (G) is a dibutyltin salt of an organic acid.